Powering Flight

The obvious answer to a cleaner and safer future is the abandonment of fossil fuels. For the production of electricity, this is already on the way. Use of coal has been cut in half just since the turn of the century and the trend continues today.

Decarbonizing surface transportation is way behind the curve, but occurring nonetheless. Projections suggest that by 2030, half the new cars on the market will be electric. In the second quarter of 2019, One electric car, the Tesla Model 3, sold more cars in its class than any other. And all the others were gasoline-powered cars.

Stationary power production and surface transportation are easy compared to flight. To practically power aircraft takes an extremely energy-dense fuel. Fossil fuels such as gasoline or jet fuel are 70 to 100 times as energy-dense as the energy stored in a rechargeable Lithium-ion battery.

The only current alternative to liquid fossil fuel is biofuel, ethanol from corn and sugar beets and biodiesel from soybeans. Ethanol makes up a scant two percent of our liquid fuel needs, biodiesel less than that. The figure is even lower than that when you account for the fossil fuel energy inputs to the production of biofuels. We won’t see row crop biofuels making up a larger share of our fuel needs because of the negative environmental impacts and the fact that biofuels production drives up food prices.

Another source of liquid fuel could be waste-to-fuel plants. There are already facilities which burn garbage (solid waste) for the generation of electricity, consuming about fifteen percent of all solid waste. Although this does produce energy and reduce the need for landfills, it doesn’t help with air transportation. There are also concerns about the environmental and health impacts of the combustion products.

Recycling has become difficult recently as China has greatly decreased accepting our wastes. Rather than simply landfilling wastes that can’t be recycled, it is possible to convert the waste to a useful fuel to power aircraft.

Various wastes , even municipal sewage waste, when heated to high temperatures produce a mixture of gasses in a process called destructive distillation. These gasses can be chemically manipulated with catalysts and turned into a liquid hydrocarbon fuel.

A model system for waste to fuel would look something like a plant sited near a current landfill. Municipal solid waste, agricultural wastes, and suburban wastes would all be brought to the processing plant where the materials would be separated . Materials which are unusable would still be landfilled.

The biggest problem with a waste-to-fuel strategy is the resource base. The best way to contain the rising cost of just about anything is to become more efficient. The easiest way to be more efficient is to reduce waste. That means a diminishing resource base. This may not be a business model that many will wish to pursue.

The only long term solution to our energy needs regardless of source or form is to use a lot less and produce what we need sustainably. We have to learn to live within our means.

Dr. Bob Allen is Emeritus Professor of Chemistry at Arkansas Tech University.

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